The subject invention is directed to a spray nozzle for controlling flow rate in precision spray applications. The spray nozzle is intended for use in a wide variety of agricultural, industrial, and residential applications.
Agrochemicals are applied to agricultural fields to control pests and to enrich the soil with nutrients. Typically, these agrochemicals are mixed with water and sprayed over a field. The efficacy of an agrochemical spray depends on various spray variables such as flow rate, droplet size, spray distribution, and the speed of the applying vehicle. Heretofore, control over these variables has been limited.
Typically, the flow rate of a spray is determined according to the general requirement of an entire field. For example, if a pesticide is being applied, a high flow rate is chosen for a field having a relatively dense infestation of pests. A lower flow rate is chosen if the infestation is mild or the crops are delicate.
Droplet size affects the travel of the spray between the sprayer and the vegetation or ground. Under optimal conditions, a spray of small droplets provides very even coverage over a given spray area. However, small droplets are more susceptible to spray drift, a condition whereby the droplets land outside of the intended spray area. Other factors that contribute to spray drift are travel speed of the sprayer, wind, humidity, ambient temperature, and sprayer height. Thus, droplet size is an important consideration when preparing to spray a field and is typically determined according to the type of chemical being sprayed, the crop being sprayed, and the aforementioned application conditions. Droplet sizes often range from 300 to 400 micrometers.
“Spray distribution” refers to the size of the spray area and the uniformity of the chemical over the spray area. Thus, spray distribution plays a significant role in the efficacy of a given application. Spray distribution is determined, in major part, by the spray pattern of each spray nozzle and the overlap of the spray patterns of adjacent nozzles.
The affect that the speed of the applying vehicle has on the density of the spray over the field is directly related, and inversely proportional, to the flow rate. For any given flow rate, an increase in vehicle speed will result in a decrease in spray density. Without a variable flow rate capability that uses vehicle speed as an entering argument, the spray density will vary as the vehicle climbs hills, makes turns, navigates tight areas, and encounters soft ground. Varying spray density adversely affects the environment, crop yields, chemical efficacy, and costs.
The importance of flow rate, droplet size, and spray distribution are well established. However, current spray systems do little to provide for the easy adjustment of these variables. Rather, a determination is made as to the optimal setting(s) for each variable prior to application, taking into consideration the aforementioned environmental factors and the characteristics of the individual field. Initial set up can be time consuming and is usually not modified until the entire field has been sprayed and a different field, having different requirements, needs to be sprayed. This practice has obvious shortcomings.
The flow rate for most available agricultural spray systems is held constant for a given application because each conventional nozzle lacks the capabilities to control droplet size and spray distribution, for a given spray pressure. In other words, with conventional nozzles, a decrease in flow rate is effected by decreasing the fluid pressure being supplied to the nozzle. A decrease in spray pressure results in an increase in droplet size and a decrease in the spray area for each given nozzle, thereby decreasing the spray distribution and the overlap between nozzles. The spray distribution is often so degraded that the adverse effects of varying the flow rate are worse than varying vehicle speed while maintaining a constant flow rate.
Nonetheless, for precision farming, it is desirable to vary the application density of agrochemicals according to potential yield, soil type, soil nutrients, soil moisture content, weeds, diseases, and field topography. Therefore, attempts at designing an effective variable flow rate nozzle have resulted in at least one commercially available product. U.S. Pat. No. 5,134,961 describes this product as employing a pulsed solenoid valve at the entrance of a conventional spray nozzle. By cycling the solenoid valves between open and closed positions, the system varies the effective flow rate of the system while maintaining a relatively constant fluid pressure. However, this system is expensive. Each spray nozzle is coupled to a separate solenoid valve while the whole spray boom is controlled by a complex control system. Additionally, despite the efforts to provide an effective variable flow rate system, the uniformity of the spray distribution nonetheless decreases dramatically as the flow rate decreases and travel speed increases, such as when it is desired to apply a light spray over a large area. Another design, described in U.S. Pat. No. 5,908,161, utilizes a metering rod and a housing to control the flow rate. One end of the metering rod has a special shape to control flow rate and to form a fan spray. Varying the position of the metering rod in the housing provides a varying flow rate. Varying spray pressure varies the position of the metering rod in the housing. The design is simple and provides a good control of flow rate. However, the resulting spray pattern of the nozzle is improper for typical overlapping broadcast applications and the droplet size is too fine for use during periods of strong winds.
It can thus be seen that a need remains for a system that allows a uniform dispersion of agrochemicals despite variances in vehicle speed. There is further a need that provides the capability of varying flow rate and dispersion density in a controlled manner while maintaining a desired droplet size and spray area. There is also a need for a variable flow rate system that is not cost prohibitive.